1. Field of the Invention
The present invention relates to an induction system for an internal combustion engine, particularly of the kind having an additional air supply passage for supplying additional air to collectors upon idling, etc. of an engine.
2. Description of the Prior Art
A prior art induction system includes two collectors for supplying air to two groups of cylinders of which firing orders are respectively discontinuous, a bypass passage or additional air supply passage bypassing a throttle valve for supplying additional air to one of the collectors and a balance hole formed in a partition wall between the collectors for supplying additional air to the other collector.
A disadvantage of the prior art induction system is that since the additional air supply passage is directly communicated with one of the collectors but indirectly with the other collector, additional air flows into the one collector easily and efficiently but not into the other collector, tending to result in uneven distribution of additional air to the collectors, unstable idling of the engine, deteriorated fuel consumption, etc.